A lithography technique for improving resolution in wafer exposure with multi-patterning has attracted attention. Since multi-patterning requires extremely high positioning accuracy in exposure, what is important is beam irradiation-position accuracy (also referred to as global positional accuracy) of an electron-beam writing apparatus for producing a mask that becomes a master plate for transferring an LSI pattern to wafers. One factor that reduces the global positional accuracy is thermal deformation of a writing object (blank) during writing.
As a heat source located near the writing object, there are a magnetic lens coil and an alignment coil of an objective lens block, a vacuum exhaust pump of a writing chamber, etc. Although measures such as heat removal with water cooling, thermal shield, etc., are taken, it is impossible to completely block thermal flow into the writing object due to thermal radiation from those heat sources. The thermal flow causes thermal deformation of the writing object during writing to reduce the global positional accuracy.